1. Field of the Invention
This invention relates to a tape tension adjusting device, and more particularly, to a device for adjusting the tension of a magnetic tape in a magnetic recording/reproducing apparatus, such as a video cassette recorder (VCR), a digital audio tape recorder (DAT) or the like.
2. Description of the Related Art
In a recording/reproducing apparatus using magnetic tape as a recording medium, such as a VCR, a DAT or the like, a magnetic tape received within a tape cassette is drawn from the tape cassette, and a recording/reproducing operation is performed while pressing the magnetic tape against a recording/reproducing magnetic head, such as a rotating head or the like.
FIG. 1 shows a tape loading mechanism of a so-called helical-scanning VCR wherein a tape is drawn from a cassette and is helically wound around a rotating head drum to perform a recording/reproducing operation.
In FIG. 1, there are shown a cassette C, a supply-side reel SR and a takeup-side reel TR.
There is also shown a main chassis 101. A rotating head drum 102 is rotatably mounted on the main chassis 101 in an inclined state at a predetermined angle, and is rotated at a high speed by a motor (not shown).
Movable tape guide posts 103-106 draw a tape 116 from the cassette C mounted on the main chassis 101, and wind it around the rotating head drum 102 to form a tape path shown in FIG. 1. The movable tape guide posts 103-106 are operated by a well-known mechanism (not shown). A fixed guide post 107 for forming the tape path is provided on the main chassis 101. A capstan 108 drives the tape 116. A pinch roller 109 presses the tape 116 against the capstan 108 to run the tape 116.
A supply-side reel mount 128 and a takeup-side reel mount 132 engage the supply-side reel SR and the takeup-side reel TR within the mounted cassette C to rotate the reels, respectively. These reel mounts 128 and 132 are rotatably driven by well-known means (not shown).
A tension regulator arm (hereinafter termed a tension arm) 110 maintains the tension of the tape 116 running along the tape path at a constant value to provide good contact of the tape 116 with head drum 102. The tension arm 110 is rotatably disposed on the main chassis 101 via a pin 110a provided at one end of the tension arm 110. A pin 112 contacting the tape 116 is provided at the other end of the tension arm 110. The tension arm 110 is biased in a direction to press the pin 112 against the tape 116 by the elasticity of spring 114, and is connected to one end of a belt 130 wound around the outer circumference of the supply-side reel mount 128.
When the tension arm 110 is biased in a counterclockwise direction direction by spring 114, the supply-side reel mount 128 is braked by surface contact with the belt 130. When the tension arm 110 rotates in a clockwise direction, the belt 130 is loosened to reduce braking action applied to the supply-side reel mount 128.
When the tape 116 runs in the state shown in FIG. 1, if back tension applied to the tape 116 is reduced due to a change in the amount of the tape 116 wound around the supply-side reel SR, the tension arm 110 is rotated in a counterclockwise direction by the spring 114 to tighten the belt 130 around reel mount 128. The back tension, i.e., the load in the tape running system, changes as the diameter of the tape 116 wound around the reel SR changes, thus changing the rotational moment in rotating reel SR. Hence, the supply-side reel mount 128 is braked to increase the back tension, and the original tension is restored.
When the back tension on the tape 116 increases, the tension arm 110 is rotated in a clockwise direction against the spring 114 to loosen the belt 130. Hence, the brake force applied against the supply-side reel mount 128 is lessened to reduce the back tension, and the original tension is recovered.
In order to perform a stable recording/reproducing operation, it is necessary to apply a predetermined tension to the tape 116. As described above, since the tension arm 110 detects a change in the tape tension and automatically corrects the tension, it is possible to always maintain the tape tension at a predetermined value.
According to the tape loading mechanism, in an unloading state wherein the tape 116 is received within the cassette C, the movable guide posts 103-106, the pinch roller 109 and the pin 112 of the tension arm 110 are situated inside the tape 116 within the cassette C, as indicated by broken lines in FIG. 1. When the tape loading mechanism operates, the movable guide posts 103-106, the pinch roller 109 and the pin 112 of the tension arm 110 draw the tape 116 from within the cassette C to provide a loading state wherein the tape path shown in FIG. 1 is formed.
The above-described tape loading mechanism, however, has the following problems.
That is, in a normal tape running state wherein the tape 116 runs in the direction of arrow A (the forward direction) shown in FIG. 1, the tape tension must be maintained constant. When the tape 116 is running, the tension arm 110 is free, and a change in the tape tension is detected to control the braking effect of the belt 130, as described above. The brake for the supply-side reel mount 128 is thereby controlled to maintain the tape tension constant.
When the tape 116 stops, the tape 116 must be loosened because the tape 116 may be damaged if an unnecessary tension is applied to the tape 116.
When the tape 116 runs in a direction reverse to the direction of arrow A (in a reversal playback operation or the like), since the capstan 108 is at a side downstream from the rotating head drum 102 in the forward running direction of the tape 116, the entire running system from the rotating head drum 102 to the takeup-side reel mount 132 becomes the rotation load, and the tape 116 is wound by the reel mount 128 which has previously been at the supply side. Accordingly, at the position of the tension arm 110, the tape 116 is pulled by the supply-side reel mount 128 to provide an excessive tension on the tape 116. As a result, the tension arm 110 is displaced by rotating in a clockwise direction against the spring 114, causing a change in the running position of the tape 116, whereby the tape 116 may be damaged by contacting the tape outlet in the cassette C.
Accordingly, the tension arm 110 must free the tape 116 when the tape 118 is running in the forward direction, restrict the tape 116 at a position where the tape 116 is loosened when the tape 116 stops, and restrict the movement of the tape 116 due to an excessive tension when the tape 116 is running in the reverse direction so that the running position of the tape 116 is not changed by the rotation of the tension arm 110 due to an increase in the tension.
In the above-described tape loading mechanism, however, the tension arm 110 is situated inside the tape 116 within the cassette C indicated by the broken lines in FIG. 1 in an unloading state, draws the tape 116 by rotating in the direction of arrow B in accordance with a tape loading operation, and is at the tape loading position shown in FIG. 1. Accordingly, it is impossible to provide means, such as a stopper or the like, for restricting the position of the tension arm 110 when the tape 116 stops or runs in the reverse direction, because such means obstructs the rotation of the tension arm 110.
Under such a background, in order to perform the position restriction in the above-described respective operational modes of the tension arm 110, there have been proposed configurations wherein the above-described stopper is separated from the rotational range of the tension arm 110 until the tape loading state is provided, and the tension arm 110 is moved to a position where it can be restricted after the tape loading operation has been completed.
FIGS. 2 and 3 show an example of such configurations. In FIGS. 2 and 3, the same components as those shown in FIG. 1 are indicated by the same reference numerals.
In FIGS. 2 and 3, a stopper arm 134 is rotatably disposed on the main chassis 101 by a pin 138. A restricting member 134a for restricting the position of the tension arm 110 is formed at one end of the stopper arm 134. A cam follower pin 134b engaging a cam groove 138a formed on a gear board 138 (to be described later) is provided at the other end of the stopper arm 134.
The cam board 138 functions as a mode control means for setting various kinds of operational modes including the tape loading mechanism shown in FIG. 1 via a well-known drive transmission mechanism (not shown), and is rotatably disposed on the main chassis 101 via a pin 140. A gear portion formed on the outer circumference of the cam board 138 meshes with gear 144 mounted on the rotation shaft of a motor 142, whereby the cam board 138 is rotated by the rotation of the motor 142 at a reduced speed.
The cam groove 138a, whose distance from the pin 140 serving as the center of rotation changes in accordance with the rotational position, is formed on the cam board 138 so as to control the rotation of the stopper arm 134 by the rotation of the cam board 138 via the cam groove 138a.
The relationship between the cam groove 138a of the cam board 138 and the stopper arm 134 will now be explained. FIG. 2 shows a state in the course of tape loading shifting from an unloading state to a tape loading state. In this state, the cam follower pin 134b of the stopper arm 134 moves along a small-diameter portion of the cam groove 138a during the unloading state and the tape loading operation, whereby the stopper arm 134 is rotated in a counterclockwise direction and the restricting member 134a is maintained at a position out of the rotational range of the tension arm 110. Accordingly, the rotation of the tension arm 110 during the tape loading operation is not obstructed.
After the tape loading operation has been completed and the tension arm 110 has rotated to its operational position, the cam follower pin 134b of the stopper arm 134 moves from the small-diameter portion to a large-diameter portion of the cam groove 138a, as shown in FIG. 3, to rotate the stopper arm 134 in a clockwise direction. Hence, the restricting member 134a is moved to a position where the rotation of the tension arm 134 can be restricted. It is thereby possible to restrict the rotational position of the tension arm 110 if an excessive tension is applied during, for example, a playback operation of the tape in the reverse direction.
In the above-described method of restricting the tension arm using the movable members, however, positional accuracy is reduced due to a clearance between the respective members and the like, whereby, for example, the stability of the tape tension is reduced, and the tape is damaged by contacting the cassette because the running position of the tape is deviated, causing a problem from the viewpoint of reliability.
Furthermore, when the tape stops, the tension arm 110 is driven in a counterclockwise direction by the spring 114 to press its pin 112 against the tape. Hence, the tension continues to be applied to the tape, causing damage to the tape as described above.
In order to solve the above-described problems, a new stopper for restricting the tension arm 110 against the spring 114 is needed. Such a stopper must be separated from the tension arm 110 in its normal position because the stopper may obstruct the rotation of the tension arm 110 during the normal tape running state, and must be in close contact with the tension arm 110 only when the tape stops. In addition, the stopper cannot be provided within the rotational range of the tension arm 110.
However, it is almost impossible to provide a movable stopper mechanism for dealing with excessive tape tension to be used when the tape is not running at both sides of the tension arm 110, in consideration of limited space, complication of the configuration, and relationship with other mechanisms. Accordingly, in the above-described tape loading mechanism, it is impossible to provide complete means for restricting the tension arm 110.